/*
 * PL/Python main entry points
 *
 * src/pl/plpython/plpy_main.c
 */

#include "postgres.h"

#include "access/htup_details.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_type.h"
#include "commands/trigger.h"
#include "executor/spi.h"
#include "miscadmin.h"
#include "utils/guc.h"
#include "utils/memutils.h"
#include "utils/rel.h"
#include "utils/syscache.h"

#include "plpython.h"

#include "plpy_main.h"

#include "plpy_elog.h"
#include "plpy_exec.h"
#include "plpy_plpymodule.h"
#include "plpy_procedure.h"
#include "plpy_subxactobject.h"


/*
 * exported functions
 */

#if PY_MAJOR_VERSION >= 3
/* Use separate names to avoid clash in pg_pltemplate */
#define plpython_validator plpython3_validator
#define plpython_call_handler plpython3_call_handler
#define plpython_inline_handler plpython3_inline_handler
#endif

extern void _PG_init(void);

PG_MODULE_MAGIC;

PG_FUNCTION_INFO_V1(plpython_validator);
PG_FUNCTION_INFO_V1(plpython_call_handler);
PG_FUNCTION_INFO_V1(plpython_inline_handler);

#if PY_MAJOR_VERSION < 3
/* Define aliases plpython2_call_handler etc */
PG_FUNCTION_INFO_V1(plpython2_validator);
PG_FUNCTION_INFO_V1(plpython2_call_handler);
PG_FUNCTION_INFO_V1(plpython2_inline_handler);
#endif


static bool PLy_procedure_is_trigger(Form_pg_proc procStruct);
static void plpython_error_callback(void *arg);
static void plpython_inline_error_callback(void *arg);
static void PLy_init_interp(void);

static PLyExecutionContext *PLy_push_execution_context(void);
static void PLy_pop_execution_context(void);

/* static state for Python library conflict detection */
static int *plpython_version_bitmask_ptr = NULL;
static int    plpython_version_bitmask = 0;

/* initialize global variables */
PyObject   *PLy_interp_globals = NULL;

/* this doesn't need to be global; use PLy_current_execution_context() */
static PLyExecutionContext *PLy_execution_contexts = NULL;


void
_PG_init(void)
{
    int          **bitmask_ptr;

    /*
     * Set up a shared bitmask variable telling which Python version(s) are
     * loaded into this process's address space.  If there's more than one, we
     * cannot call into libpython for fear of causing crashes.  But postpone
     * the actual failure for later, so that operations like pg_restore can
     * load more than one plpython library so long as they don't try to do
     * anything much with the language.
     */
    bitmask_ptr = (int **) find_rendezvous_variable("plpython_version_bitmask");
    if (!(*bitmask_ptr))        /* am I the first? */
        *bitmask_ptr = &plpython_version_bitmask;
    /* Retain pointer to the agreed-on shared variable ... */
    plpython_version_bitmask_ptr = *bitmask_ptr;
    /* ... and announce my presence */
    *plpython_version_bitmask_ptr |= (1 << PY_MAJOR_VERSION);

    /*
     * This should be safe even in the presence of conflicting plpythons, and
     * it's necessary to do it before possibly throwing a conflict error, or
     * the error message won't get localized.
     */
    pg_bindtextdomain(TEXTDOMAIN);
}

/*
 * Perform one-time setup of PL/Python, after checking for a conflict
 * with other versions of Python.
 */
static void
PLy_initialize(void)
{
    static bool inited = false;

    /*
     * Check for multiple Python libraries before actively doing anything with
     * libpython.  This must be repeated on each entry to PL/Python, in case a
     * conflicting library got loaded since we last looked.
     *
     * It is attractive to weaken this error from FATAL to ERROR, but there
     * would be corner cases, so it seems best to be conservative.
     */
    if (*plpython_version_bitmask_ptr != (1 << PY_MAJOR_VERSION))
        ereport(FATAL,
                (errmsg("multiple Python libraries are present in session"),
                 errdetail("Only one Python major version can be used in one session.")));

    /* The rest should only be done once per session */
    if (inited)
        return;

#if PY_MAJOR_VERSION >= 3
    PyImport_AppendInittab("plpy", PyInit_plpy);
#endif
    Py_Initialize();
#if PY_MAJOR_VERSION >= 3
    PyImport_ImportModule("plpy");
#endif
    PLy_init_interp();
    PLy_init_plpy();
    if (PyErr_Occurred())
        PLy_elog(FATAL, "untrapped error in initialization");

    init_procedure_caches();

    explicit_subtransactions = NIL;

    PLy_execution_contexts = NULL;

    inited = true;
}

/*
 * This should be called only once, from PLy_initialize. Initialize the Python
 * interpreter and global data.
 */
static void
PLy_init_interp(void)
{
    static PyObject *PLy_interp_safe_globals = NULL;
    PyObject   *mainmod;

    mainmod = PyImport_AddModule("__main__");
    if (mainmod == NULL || PyErr_Occurred())
        PLy_elog(ERROR, "could not import \"__main__\" module");
    Py_INCREF(mainmod);
    PLy_interp_globals = PyModule_GetDict(mainmod);
    PLy_interp_safe_globals = PyDict_New();
    if (PLy_interp_safe_globals == NULL)
        PLy_elog(ERROR, "could not create globals");
    PyDict_SetItemString(PLy_interp_globals, "GD", PLy_interp_safe_globals);
    Py_DECREF(mainmod);
    if (PLy_interp_globals == NULL || PyErr_Occurred())
        PLy_elog(ERROR, "could not initialize globals");
}

Datum
plpython_validator(PG_FUNCTION_ARGS)
{
    Oid            funcoid = PG_GETARG_OID(0);
    HeapTuple    tuple;
    Form_pg_proc procStruct;
    bool        is_trigger;

    if (!CheckFunctionValidatorAccess(fcinfo->flinfo->fn_oid, funcoid))
        PG_RETURN_VOID();

    if (!check_function_bodies)
        PG_RETURN_VOID();

    /* Do this only after making sure we need to do something */
    PLy_initialize();

    /* Get the new function's pg_proc entry */
    tuple = SearchSysCache1(PROCOID, ObjectIdGetDatum(funcoid));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for function %u", funcoid);
    procStruct = (Form_pg_proc) GETSTRUCT(tuple);

    is_trigger = PLy_procedure_is_trigger(procStruct);

    ReleaseSysCache(tuple);

    /* We can't validate triggers against any particular table ... */
    PLy_procedure_get(funcoid, InvalidOid, is_trigger);

    PG_RETURN_VOID();
}

#if PY_MAJOR_VERSION < 3
Datum
plpython2_validator(PG_FUNCTION_ARGS)
{
    /* call plpython validator with our fcinfo so it gets our oid */
    return plpython_validator(fcinfo);
}
#endif                            /* PY_MAJOR_VERSION < 3 */

Datum
plpython_call_handler(PG_FUNCTION_ARGS)
{
    Datum        retval;
    PLyExecutionContext *exec_ctx;
    ErrorContextCallback plerrcontext;

    PLy_initialize();

    /* Note: SPI_finish() happens in plpy_exec.c, which is dubious design */
    if (SPI_connect() != SPI_OK_CONNECT)
        elog(ERROR, "SPI_connect failed");

    /*
     * Push execution context onto stack.  It is important that this get
     * popped again, so avoid putting anything that could throw error between
     * here and the PG_TRY.  (plpython_error_callback expects the stack entry
     * to be there, so we have to make the context first.)
     */
    exec_ctx = PLy_push_execution_context();

    /*
     * Setup error traceback support for ereport()
     */
    plerrcontext.callback = plpython_error_callback;
    plerrcontext.previous = error_context_stack;
    error_context_stack = &plerrcontext;

    PG_TRY();
    {
        Oid            funcoid = fcinfo->flinfo->fn_oid;
        PLyProcedure *proc;

        if (CALLED_AS_TRIGGER(fcinfo))
        {
            Relation    tgrel = ((TriggerData *) fcinfo->context)->tg_relation;
            HeapTuple    trv;

            proc = PLy_procedure_get(funcoid, RelationGetRelid(tgrel), true);
            exec_ctx->curr_proc = proc;
            trv = PLy_exec_trigger(fcinfo, proc);
            retval = PointerGetDatum(trv);
        }
        else
        {
            proc = PLy_procedure_get(funcoid, InvalidOid, false);
            exec_ctx->curr_proc = proc;
            retval = PLy_exec_function(fcinfo, proc);
        }
    }
    PG_CATCH();
    {
        PLy_pop_execution_context();
        PyErr_Clear();
        PG_RE_THROW();
    }
    PG_END_TRY();

    /* Pop the error context stack */
    error_context_stack = plerrcontext.previous;
    /* ... and then the execution context */
    PLy_pop_execution_context();

    return retval;
}

#if PY_MAJOR_VERSION < 3
Datum
plpython2_call_handler(PG_FUNCTION_ARGS)
{
    return plpython_call_handler(fcinfo);
}
#endif                            /* PY_MAJOR_VERSION < 3 */

Datum
plpython_inline_handler(PG_FUNCTION_ARGS)
{
    InlineCodeBlock *codeblock = (InlineCodeBlock *) DatumGetPointer(PG_GETARG_DATUM(0));
    FunctionCallInfoData fake_fcinfo;
    FmgrInfo    flinfo;
    PLyProcedure proc;
    PLyExecutionContext *exec_ctx;
    ErrorContextCallback plerrcontext;

    PLy_initialize();

    /* Note: SPI_finish() happens in plpy_exec.c, which is dubious design */
    if (SPI_connect() != SPI_OK_CONNECT)
        elog(ERROR, "SPI_connect failed");

    MemSet(&fake_fcinfo, 0, sizeof(fake_fcinfo));
    MemSet(&flinfo, 0, sizeof(flinfo));
    fake_fcinfo.flinfo = &flinfo;
    flinfo.fn_oid = InvalidOid;
    flinfo.fn_mcxt = CurrentMemoryContext;

    MemSet(&proc, 0, sizeof(PLyProcedure));
    proc.mcxt = AllocSetContextCreate(TopMemoryContext,
                                      "__plpython_inline_block",
                                      ALLOCSET_DEFAULT_SIZES);
    proc.pyname = MemoryContextStrdup(proc.mcxt, "__plpython_inline_block");
    proc.langid = codeblock->langOid;
    proc.result.out.d.typoid = VOIDOID;

    /*
     * Push execution context onto stack.  It is important that this get
     * popped again, so avoid putting anything that could throw error between
     * here and the PG_TRY.  (plpython_inline_error_callback doesn't currently
     * need the stack entry, but for consistency with plpython_call_handler we
     * do it in this order.)
     */
    exec_ctx = PLy_push_execution_context();

    /*
     * Setup error traceback support for ereport()
     */
    plerrcontext.callback = plpython_inline_error_callback;
    plerrcontext.previous = error_context_stack;
    error_context_stack = &plerrcontext;

    PG_TRY();
    {
        PLy_procedure_compile(&proc, codeblock->source_text);
        exec_ctx->curr_proc = &proc;
        PLy_exec_function(&fake_fcinfo, &proc);
    }
    PG_CATCH();
    {
        PLy_pop_execution_context();
        PLy_procedure_delete(&proc);
        PyErr_Clear();
        PG_RE_THROW();
    }
    PG_END_TRY();

    /* Pop the error context stack */
    error_context_stack = plerrcontext.previous;
    /* ... and then the execution context */
    PLy_pop_execution_context();

    /* Now clean up the transient procedure we made */
    PLy_procedure_delete(&proc);

    PG_RETURN_VOID();
}

#if PY_MAJOR_VERSION < 3
Datum
plpython2_inline_handler(PG_FUNCTION_ARGS)
{
    return plpython_inline_handler(fcinfo);
}
#endif                            /* PY_MAJOR_VERSION < 3 */

static bool
PLy_procedure_is_trigger(Form_pg_proc procStruct)
{
    return (procStruct->prorettype == TRIGGEROID ||
            (procStruct->prorettype == OPAQUEOID &&
             procStruct->pronargs == 0));
}

static void
plpython_error_callback(void *arg)
{
    PLyExecutionContext *exec_ctx = PLy_current_execution_context();

    if (exec_ctx->curr_proc)
        errcontext("PL/Python function \"%s\"",
                   PLy_procedure_name(exec_ctx->curr_proc));
}

static void
plpython_inline_error_callback(void *arg)
{
    errcontext("PL/Python anonymous code block");
}

PLyExecutionContext *
PLy_current_execution_context(void)
{
    if (PLy_execution_contexts == NULL)
        elog(ERROR, "no Python function is currently executing");

    return PLy_execution_contexts;
}

MemoryContext
PLy_get_scratch_context(PLyExecutionContext *context)
{
    /*
     * A scratch context might never be needed in a given plpython procedure,
     * so allocate it on first request.
     */
    if (context->scratch_ctx == NULL)
        context->scratch_ctx =
            AllocSetContextCreate(TopTransactionContext,
                                  "PL/Python scratch context",
                                  ALLOCSET_DEFAULT_SIZES);
    return context->scratch_ctx;
}

static PLyExecutionContext *
PLy_push_execution_context(void)
{
    PLyExecutionContext *context;

    context = (PLyExecutionContext *)
        MemoryContextAlloc(TopTransactionContext, sizeof(PLyExecutionContext));
    context->curr_proc = NULL;
    context->scratch_ctx = NULL;
    context->next = PLy_execution_contexts;
    PLy_execution_contexts = context;
    return context;
}

static void
PLy_pop_execution_context(void)
{
    PLyExecutionContext *context = PLy_execution_contexts;

    if (context == NULL)
        elog(ERROR, "no Python function is currently executing");

    PLy_execution_contexts = context->next;

    if (context->scratch_ctx)
        MemoryContextDelete(context->scratch_ctx);
    pfree(context);
}
